In the oil and gas industry, hydrocarbons are obtained from subterranean geologic formations by drilling a well that penetrates one or more hydrocarbon-bearing formations. The well provides a flowpath for the hydrocarbons to reach the surface, and production of the hydrocarbons to the surface occurs when a sufficiently unimpeded flowpath from the hydrocarbon-bearing formation to the wellbore is present.
The majority of subterranean formations produced today have low natural permeability. To improve permeability and well productivity, hydrocarbon-bearing formations are commonly subjected to a hydraulic fracturing operation, also commonly referred to as “fracking.” Hydraulic fracturing entails pumping a fracturing fluid downhole under high pressure and high flow rates and injecting the fracturing fluid into adjacent hydrocarbon-bearing formations to create, open, and extend formation fractures. Fracturing fluids usually contain propping agents, commonly referred to as “proppant” or “proppant particulates,” that are carried into the fractures and deposited to hold or “prop” open the fractures once the fluid pressure is reduced. Propping the fractures open enhances permeability by allowing the fractures to serve as conduits for hydrocarbons trapped within the formation to flow to the wellbore.
Most fracturing fluids contain one or more additives to viscosify the fracturing fluid and thereby aid in transporting the fracturing fluid and proppant deeper into the fractures. Common viscosifying additives include hydrophilic polymers and guar. Preferred viscosity levels for the fracturing fluids are reached when the viscosifying additive becomes properly hydrated. The term “hydration” refers to the process wherein a hydratable material solvates or absorbs water (hydrates) and swells in the presence of water. Most commonly, a viscosifying additive is added to a fracturing fluid from a non-hydrated or poorly hydrated concentrate. High-shear blending protocols may provide more effective polymer hydration but result in polymer chain scission, which reduces the viscosity of the fluid and compromises the ability of the polymer to transport the proppant. Further, in most instances, conventional fracturing fluid formulation processes do not result in instantaneous hydration, thereby necessitating a wait time or multistage hydration protocol. Moreover, high-shear mixing (blending) may or may not cause a reduction in viscosity but it will damage the structure of the polymer, which can translate to a reduced ability to transport proppant.
As an alternative to waiting, slower hydrating polymers (e.g., guar gum) and faster hydrating polyacrylamides do not go through a pre-hydration step but rather are expected to hydrate “on the fly” as they are pumped. These polymers complete their hydration either in the tubular goods or early in the fracture. This approach currently is necessary to save time and labor but may not result in obtaining maximum performance properties out of the polymer and the concentration that is being utilized.
Multistage hydration protocols used to generate high viscosity fracturing fluids can be challenging, particularly at remote sites or when large fluid and proppant volumes are required. Special equipment for mixing the dry additives with water is required, and problems such as chemical dusting, uneven mixing, and lumping can often result. Lumping occurs when the initial contact of the dry additive with the water results in rapid hydration of the outer layer of the material, which creates a sticky, rubbery exterior layer that prevents the interior portions of the material from contacting the water. The result is the formation of “gel balls” or “fish eyes,” which can encumber efficiency by lowering the viscosity achieved per pound of dry additive and also by creating insoluble particles that can restrict flow both into and out of the subterranean formations. Consequently, merely mixing the dry additive directly with water often does not generate a homogeneous fracturing fluid, which is one reason why liquid forms of the polymers (e.g., concentrates) are preferred.
Thus, there is still a need in the art for more effective systems and methods for hydrating dry additives used in the production of fracturing fluids.